Furnace



FIG. 1 is a front perspective view illustrating the design for a furnace;

FIG. 2 is a rear view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a side view thereof;

FIG. 5 is a side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof. 

CLAIM The ornamental design for a furnace, as shown and described. 